Irrigation control systems and sprinkler control systems are known in the art. Some of the known sprinkler and irrigation control systems are operated manually. Many of the known irrigation or sprinkler control systems utilize timers to activate and deactivate the sprinkler valves. These timers are either mechanically or electrically operated, and activate the sprinkler valves at a predetermined time for a predetermined period of time. A disadvantage of this type of automatic sprinkler control system is that the system does not account for the level of moisture present in the soil before the sprinklers are activated. Therefore, the sprinkler valves activate whether or not the soil requires watering. For example, the sprinkler valves will automatically activate during a rainstorm, even though the soil does not require watering. Also, because the sprinkler valves turn off automatically after a predetermined amount of time, the soil may not be adequately watered before the sprinklers are deactivated.
The timer controlled sprinkler and irrigation control systems therefore, are inefficient in at least three ways. Firstly, the landscaping is not properly irrigated or watered. Instead, the landscaping is frequently either underwatered or overwatered. Secondly, if the sprinkler valves are activated when the soil is already sufficiently moist, the water from the sprinkler valves creates run-off and water waste.
Thirdly, with most automatic sprinkling systems, the water is applied to the ground faster and in a greater quantity than the ground is capable of absorbing. As a result, many automatic sprinklers create run-off or flooding even when used under ideal conditions. The second and third above-described problems are especially of concern in geographical regions suffering from water shortages or drought.
In order to overcome these problems with the timer controlled sprinkler systems, automatic sprinkling control systems that include soil moisture probes were designed. These systems use probes inserted into the soil to measure moisture in the ground. The soil moisture sensors measure either the resistance or the capacitance level in the soil, which corresponds to the level of moisture in the soil. The sprinkler valves are activated when the probe detects a lack of moisture, and the sprinkler valves are deactivated when sufficient soil moisture is detected.
However, the soil moisture probe sprinkler control systems are also subject to certain disadvantages due to the inefficiencies of the soil moisture sensors. Firstly, the soil moisture sensors, in order to properly measure the soil moisture content, are inserted to a certain depth into the soil. However, the water from the sprinkler valves requires a significant period of time to soak from the top surface of the ground down into the soil. Depending on the depth of insertion for the soil moisture probes, it may require several minutes for the water to soak into the soil surrounding the contacts. As a result, by the time the soil moisture probes detect a sufficient level of moisture, the ground has already been over-watered for several minutes. This problem creates overwatering, water waste, and water run-off.
A second disadvantage of many of the soil moisture sensors used in the prior irrigation control systems is that the system applies a direct voltage across the sensors in order to measure the level of resistance or capacitance in the soil. The application of direct current to the sensors causes electrolysis and hydrolysis at the sensor. The hydrolysis and electrolysis effect breaks the bond between hydrogen and oxygen in the soil moisture. In turn, the hydrogen ion both causes conduction and enhances the ionization of chloride in the salts in the soil. Therefore, after time, the direct current type of sensor is not sensing water, but the ionized salts. Furthermore, the ionized salts are not necessarily proportional to the moisture in the soil in that region. The buildup due to electrolysis adjacent the sensor tends to increase the electrical transmissivity of that portion of the soil due to ionization. This increase in ionization in that region disturbs the reading so that the direct current through the probe is not proportional to the water moisture. As a result, the current stays the same while the soil becomes less moist over a period of time. Eventually, the sensor becomes conductive even though the soil is quite dry in the region of the sensor. Therefore the use of direct current with the soil moisture sensors is not reliable over an extended period of time.
Moreover, the soil moisture sensor sprinkling systems have not solved the problem wherein water is applied to the ground faster than the ground can absorb the water. Therefore, the soil moisture sensor systems can still result in undesired run-off, flooding, and water waste.
Therefore, a need exists for an improved irrigation control system that applies alternating current to soil moisture sensors to determine whether the soil has reached a pre-determined level of saturation or dryness, and pulses the sprinklers when the pre-determined level of soil dryness is reached, and deactivates the sprinklers when a predetermined level of soil saturation is reached.